AttAcc! Unleashing the Power of PIM for Batched Transformer-based Generative Model Inference

The Transformer-based generative model (TbGM), comprising summarization (Sum) and generation (Gen) stages, has demonstrated unprecedented generative performance across a wide range of applications. However, it also demands immense amounts of compute and memory resources. Especially, the Gen stages, consisting of the attention and fully-connected (FC) layers, dominate the overall execution time. Meanwhile, we reveal that the conventional system with GPUs used for TbGM inference cannot efficiently execute the attention layer, even with batching, due to various constraints. To address this inefficiency, we first propose AttAcc, a processing-in-memory (PIM) architecture for efficient execution of the attention layer. Subsequently, for the end-to-end acceleration of TbGM inference, we propose a novel heterogeneous system architecture and optimizations that strategically use xPU and PIM together. It leverages the high memory bandwidth of AttAcc for the attention layer and the powerful compute capability of the conventional system for the FC layer. Lastly, we demonstrate that our GPU-PIM system outperforms the conventional system with the same memory capacity, improving performance and energy efficiency of running a 175B TbGM by up to 2.81× and 2.67×, respectively.